var nums = [1, 2, 3, 4, 5]

function doubleAll(array) {
    return _.map(array, function(n) {
        return n * 2;
    });
}

var doubleAllResult = doubleAll(nums);
console.log(doubleAllResult); // [2, 4, 6, 8, 10]

function sumArray(array) {
    return _.reduce(array, function(a, b) {
        return a + b;
    });
}

var sumArrayResult = sumArray(nums);
console.log(sumArrayResult); // 15

function onlyEven(array) {
    return _.filter(array, function(n) {
        return (n % 2) === 0;
    });
}

var onlyEvenResult = onlyEven(nums);
console.log(onlyEvenResult); // [2, 4]